1. Field of the Invention
The present invention relates to a high-frequency laminated component realizing a desired circuit function by providing electrodes in predetermined patterns on a plurality of insulating layers, and also relates to a laminated high-frequency filter including the high-frequency laminated component.
2. Description of the Related Art
In the past, various types of high-frequency laminated components have been used in wireless devices, such as cellular phones. As indicated in Japanese Unexamined Patent Application Publication No. 8-46401, for example, a high-frequency laminated component has a laminated structure including a plurality of insulating layers.
In the high-frequency laminated component, predetermined electrode patterns are formed on the plurality of insulating layers to form inductors and capacitors. Further, the inductors and the capacitors formed by these electrode patterns are connected by other electrode patterns to realize a circuit function, such as a band pass filter, for example.
The above-described high-frequency laminated component is used as mounted on or in another circuit board, and thus includes terminal electrodes for mounting. The terminal electrodes are normally formed on end surfaces (side surfaces) or a bottom surface of the high-frequency laminated component. It is therefore necessary to provide routing electrodes for connecting the electrode patterns forming a circuit function section, which includes the above-described inductors and capacitors, and the terminal electrodes. For example, in Japanese Unexamined Patent Application Publication No. 8-46401, to connect electrode patterns on a predetermined layer to a ground electrode on a bottom surface, electrodes for connecting these elements are formed on end surfaces (side surfaces) of a laminate.
Meanwhile, in the laminated structure described in Japanese Unexamined Patent Application Publication No. 8-46401, for example, the routing electrodes between the electrodes forming the circuit function section and the ground electrode are increased in length, and the influence of a parasitic inductor Lg is increased. If the parasitic inductor Lg is present, the attenuation characteristic in a high-frequency band is deteriorated. Therefore, a desired transmission characteristic fails to be obtained, even if the laminated structure configures a filter, such as a band pass filter, for example.
As a method of solving above-described problem of the parasitic inductor Lg, a ground impedance adjustment circuit as illustrated in FIG. 1 is provided. FIG. 1 illustrates an equivalent circuit of a high-frequency laminated component including a ground impedance adjustment circuit.
As illustrated in FIG. 1, the high-frequency laminated component includes first and second input/output terminals Pio1 and Pio2, a circuit function section, and a parasitic inductor Lg, and also includes a ground impedance adjustment circuit having three capacitors C1, C2, and C12 connected in a π-shape. With the provision of the above-described ground impedance adjustment circuit, it is possible to form an attenuation pole in a desired frequency band, and thus to prevent the deterioration of the attenuation characteristic in a high-frequency band due to the parasitic inductor Lg.
Further, as a laminated high-frequency filter formed by a high-frequency laminated component similarly having a plurality of insulating layers laminated, there is a structure described in International Publication No. WO 2007-119356, for example.
In a laminated high-frequency filter described in International Publication No. WO 2007-119356, predetermined electrode patterns are formed on a plurality of insulating layers to form inductors and capacitors. The inductors and the capacitors formed by these electrode patterns form a plurality of LC resonators. In the plurality of LC resonators, LC resonators on the opposite sides are respectively connected to input/output terminals, and the respective inductors of adjacent LC resonators are electromagnetic field-coupled. Thereby, a filter circuit including a plurality of stages of LC resonators is formed.
The above-described filter circuit occasionally includes a skip-coupling capacitor for capacitance-coupling the input/output terminals on the opposite sides by skipping a plurality of stages of LC resonators, to thereby obtain a desired characteristic.
Further, an electrode forming the skip-coupling capacitor is formed into an elongated shape extending in a direction of connecting opposite end portions of a laminate formed with input/output electrodes serving as the input/output terminals, as in an electrode indicated as 160 in FIG. 42 and an electrode indicated as 260 in FIG. 45 of International Publication No. WO 2007-119356.
When the above-described ground impedance adjustment circuit is formed on or in a laminated substrate, however, the following problem arises. FIG. 2 is a diagram illustrating a laminate 10P of a conventional ground impedance adjustment circuit. FIG. 3 is a diagram illustrating a transmission characteristic of the ground impedance adjustment circuit having the structure of FIG. 2. FIG. 4A is an equivalent circuit diagram of a band pass filter including three stages of LC resonators. FIG. 4B is a transmission characteristic diagram of a case where the band pass filter illustrated in FIG. 4A is configured with the use of the ground impedance adjustment circuit having the conventional structure.
As illustrated in FIG. 2, the laminate 10P of the ground impedance adjustment circuit has a laminated structure of five insulating layers 901P to 905P. The lowermost (first) insulating layer 901P is formed with input/output electrodes 201 and 202 and a ground electrode 110. The ground electrode 110 is formed on a bottom surface of the insulating layer 901P, and the input/output electrodes 201 and 202 are formed to respectively extend from two facing end surfaces of the insulating layer 901P to the bottom surface. The input/output electrodes 201 and 202 are formed on the end surfaces of the respective layers excluding the uppermost (fifth) insulating layer 905P.
The second insulating layer 902P is formed with an inner-layer ground electrode 120. The inner-layer ground electrode 120 is connected to the ground electrode 110 by conductive via holes.
The third insulating layer 903P is formed with capacitor electrodes 131 and 132, and is further formed with a routing electrode for connecting the capacitor electrode 131 and the not-illustrated input/output electrode 201 and a routing electrode for connecting the capacitor electrode 132 and the input/output electrode 202.
The fourth insulating layer 904P is formed with a capacitor electrode 140.
With the above-described structure, a region in which the capacitor electrode 131 and the inner-layer ground electrode 120 face each other corresponds to the capacitor C1 in FIG. 1. A region in which the capacitor electrode 132 and the inner-layer ground electrode 120 face each other corresponds to the capacitor C2 in FIG. 1. A region in which the capacitor electrode 140 and the capacitor electrodes 131 and 132 face each other corresponds to the capacitor C12 in FIG. 1. Further, when a device including this ground impedance adjustment circuit is mounted on or in a printed board or the like, the potential difference between the ground potential of the printed board and the ground potential of the ground impedance adjustment circuit corresponds to the parasitic inductor Lg. In the above-described configuration, therefore, an inductor due to the via holes is included in the parasitic inductor Lg.
As illustrated in FIG. 3, in the above-described structure, the capacitors forming the ground impedance adjustment circuit have a self-resonance point in a high-frequency band, which is caused particularly by the capacitors C1 and C2. The capacitors C1 and C2 are coupled by the capacitor C12, and thereby the transmission characteristic, which is supposed to have been improved, is locally deteriorated. For example, in the capacitor C1, the self-resonance occurs owing to residual inductance of the capacitor electrode 131 and capacitance formed between the capacitor electrode 131 and the ground electrode 120.
Therefore, even if the band pass filter as illustrated in FIG. 4A is configured with the use of the above-described ground impedance adjustment circuit, a resonance point is generated in an attenuation band, as illustrated in FIG. 4B, and a favorable frequency characteristic fails to be obtained.
Further, as indicated in International Publication No. WO 2007-119356, the electrodes forming the inductors of the LC resonators are disposed at predetermined intervals along the direction of connecting the aforementioned opposite end portions. If an electrode forming the skip-coupling capacitor has the above-described shape, therefore, the electrode is provided across a plurality of electrodes for inductors, as viewed in the lamination direction.
In the above-described structure, the electrode forming the skip-coupling capacitor exerts substantial influence on the coupling between the inductors, and the insertion loss is increased. Thereby, characteristics of the filter (transmission characteristic and attenuation characteristic) are deteriorated.